Various techniques have been utilized in the past in an attempt to gasify anesthetic liquids or moistening liquids to be applied directly into fresh gas streams. For example, U.S. Pat. Nos. 3,251,361 and 4,038,980, as well as Swedish Patent Application Ser. No. 84.03447-9, disclose various such systems. In these systems, however, it has proven difficult to provide uniform and controllable dosages from such systems. In U.S. Pat. No. 4,038,980, for example, an air humidifier 2 is employed in which water is fed from a reservoir 50 through insert 32 for evaporation upon contact with a heated sheath 22, which is maintained at a temperature of between about 200.degree. to 300.degree. C. The humidifier itself is contained within an inspiraton line, which cannot be said to be maintained at a constant pressure. Other attempts have been made to effectuate the gasification of anesthetic liquids in separate gasification chambers where both gas and liquid phases exist simultaneously. In connection with these attempts, however, problems have arisen in connection with refilling these chambers with fresh liquid. In accordance with the present invention, however, these and other problems have now been solved in a surprisingly simple manner.